Dimmable ballast systems provide varying levels of light output through a variety of means. For multi-lamp fixtures, conventional dimming ballast techniques include discrete dimming (so-called “step-dimming”) and continuous dimming. One example of discrete dimming is a multiple-lamp discrete ballast in which one or more lamps are shut off to provide a lower light output. This is sometimes implemented using external controls to turn off individual ballasts or fixtures until the selected light level is achieved. Discrete dimming approaches, however, only provide a finite number of predefined lighting levels and transitions between these discrete levels are often perceptible by users. Some continuous dimming designs operate multiple lamps in series with the power applied to the lamps being reduced for dimming. Series-connected dimming ballasts, however, suffer from inability to produce light when one or more lamps fail. Other proposed approaches include varying a DC bus amplitude via pulse width modulation (PWM) control to power a voltage or current fed inverter for driving one or more lamps, but this dimming control technique adds cost and may not provide the desired amount of dimming for certain applications. Also, continuous dimming techniques can cause early cathode failure by dimming a lamp if no separate cathode heating power is provided to keep the cathode operating within its normal temperature range. However, separate cathode heating contributes to inefficiency at dimming levels below a critical arc power level since the cathode heating power supply loss is in addition to the fact that the lamp light output is not linearly proportional to the lamp power (i.e. it may take 75% lamp power to provide 50% lamp lumens.) Thus, conventional continuous dimming techniques can lead to premature lamp degradation or failure through undesirable lamp cooling and/or extinguishment unless additional cost is incurred for cathode heating to prevent premature lamp degradation caused by the dimming operation. Continuous dimming ballasts, moreover, suffer from reduced power efficiency. Thus, there is a need for improved fluorescent lamp dimming apparatus and techniques for efficiently providing varying lighting levels to match a desired lighting level while maintaining high efficiency and without lamp stress or damage or increased cost, thereby allowing a user to selectively achieve energy savings by dimming lighting installations.